Point to Point (SCPC) VSAT links

Introduction

Single Channel per Carrier (SCPC)
technology provides dedicated, point to point connectivity using Very Small
Aperture Terminals (VSAT), making it the wireless equivalent of conventional
leased lines. Using SCPC, communication links can be provisioned anywhere in
the world with typical bandwidth rates ranging from 64 kbps to 2048 kbps.

Components

The typical components of a SCPC
link are the Ground Segment and the Space Segment.

Radio Frequency Terminal (RFT): performs Frequency Up
Conversion, Frequency Down Conversion and RF Signal Power Amplification

Satellite Modem: performs various functions including
modulation/demodulation and Error Correction

Terminal Equipment: includes the routers/switches,
servers and hosts on the customer’s network

Space
Segment

Each satellite in orbit carries a
number of transponders, with each transponder supporting typically 40 MHz of
bandwidth. This bandwidth is divided into separate channels using Frequency
Division Multiple Access (FDMA). Depending on the requirements, different number
of channels with various bandwidths can be allocated to the respective
customers. The channel(s) and associated bandwidth leased to the customer(s)
comprises the Space Segment.

Additionally, SCPC VSAT
communication utilizes Geostationary satellites. Orbiting at the height of
35,786 km above the equator, the Geostationary satellite travels in the same
direction and at the same speed as the Earth's rotation on its axis, taking 24
hours to complete a full trip around the globe. Thus, as long as a satellite is
positioned over the equator in an assigned orbital location, it will appear to
be "stationary" with respect to a specific location on the Earth. A
single SCPC VSAT link can provide connectivity for any two sites located within
the footprint (coverage area) of a Geostationary satellite.

Features

Distance Independent: links can be provisioned between
any two points within the footprint of a satellite. With typical satellite
footprints covering thousands of square kilometers and spanning multiple
countries, the technology is essentially distance independent

Quick deployment and commissioning: typical deployment
time for a link (possibly spanning thousands of kilometers) is only two to
three days. This enables rapid response to market needs.

- Following are some of the
considerations when using Ku-Band for SCPC links

o Higher Rain Attenuation

o Higher Space Segment Cost

o Limited Coverage Area

Antenna types: Various antenna types are used for SCPC
link operation. The three most commonly used types are described below

Parabolic/Center feed: The parabolic shape of the dish
reflects the signal to the dish’s focal point. Mounted on brackets at the
dish's focal point is a device called a feedhorn. This feedhorn is the
front-end of a waveguide that gathers the signals at or near the focal
point

Cassegrain: In a Cassegrain antenna, the
parabolic shape of the dish reflects the signal to the dish’s focal point.
Mounted on brackets at the dish's focal point is a secondary reflector (or
sub-reflector). This secondary reflector directs the signal towards the
feedhorn

Offset feed: In an offset antenna, the reflector
focuses the signals on to a point that is offset from the center of
the antenna.

Antenna Sizes: The typical antenna sizes (diameter) are
as follows

C-band: 1.8 - 2.4 m

Ku-band: 1.2 - 1.8 m

lnterfaces: a variety of interfaces are available on
SCPC links including Ethernet, G.703 (T1, E1, T3 and E3) and Serial
interfaces (EIA-422 and EIA-232, HSSI, V.35)